Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRICAL CONNECTORS FOR ZONE 2 HAZARDOUS LOCATIONS
TECHNICAL FIELD
[0001] This invention pertains to the field of electrical connections in
hazardous
locations where explosive gas may be present.
BACKGROUND
[0002] Most electrical plugs and receptacles are rated for use in ordinary
locations, where
explosive gas is not present. A spark can occur if current is flowing from the
receptacle to the
plug when the plug is disconnected from the receptacle. In a similar fashion,
a spark can occur
when a plug is first inserted into a receptacle. The National Electrical
Manufacturer's Association
(NEMA) defines several standards for ordinary-location plugs and receptacles.
These standards
are followed by most manufacturers. NEMA plugs and receptacles for ordinary
locations are
readily available and inexpensive.
[0003] A spark that occurs upon connection or disconnection can cause an
explosion if
explosive gas is present. For that reason, NEMA plugs and receptacles rated
for ordinary non-
hazardous locations are not normally permitted in hazardous locations where
explosive gas might
be present.
[0004] There are known examples of Explosion-Proof electrical plugs and
receptacles
intended for use in hazardous areas. These connectors are designed to allow
explosive gas to be
present in arcing and sparking equipment. The connectors are built strong
enough to contain the
resulting explosion and prevent it from propagating outside the connector.
However, these
connectors are large, heavy, and expensive. US patent 7,537,472 shows one
example of an
explosion-proof plug and receptacle typical of the prior art. US patent
2,697,212 shows another
example.
[0005] There are many known examples of electrical receptacles that keep
power
disconnected until a plug is inserted. US patent 8,770,998 uses an optical
sensor to detect when a
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plug is fully inserted, and a relay to energize the receptacle at that time.
However, this receptacle
is not safe for use in a hazardous location where explosive gas may be
present. The relay
contacts can create a spark upon opening and closing. Also, there is a race
condition when the
plug is removed. If the relay contacts have not completely opened before the
plug prongs
disconnect from the receptacle connections, a spark can occur. Either of these
sparking
conditions could cause an explosion if explosive gas is present. In addition,
the plug is not locked
into the receptacle, so unintended disconnection might occur and cause a
spark.
[0006] US patent 6,678,131 describes arc-safe electrical receptacles. This
design uses a
switch to detect the presence of the plug and a relay to connect power to the
plug and receptacle.
However, these receptacles are not safe for use in hazardous locations. The
relay contacts and the
switch can both create sparks that can ignite explosive gas. In addition, the
plug is not locked
into the receptacle, so unintended disconnection might occur and cause a
spark.
[0007] US patent 8,926,350 describes a protective lockable female
electrical outlet. This
design uses sliding contacts to energize the receptacle when a plug is
inserted. It has the
advantage of locking the plug into the receptacle to prevent unintended
disconnection. However,
the sliding contacts can create sparks that can ignite explosive gas.
[0008] US patent 8,062,069 describes a spark-free improved connector. This
design uses
a reed switch controlled by a magnet attached to a plunger to disconnect power
from the contacts
before they are separated. This design would be safe for use in a location
containing explosive
gas. However, reed switches are able to carry only very small currents. This
design is intended
mainly for communication systems where the current through the connectors is
low. This design
would not be capable of carrying 15 to 30 Amperes as required for industrial
power distribution
in hazardous locations. Also, this design does not use standard NEMA plugs and
receptacles.
[0009] US patent 4,591,732 uses a light barrier to signal a relay when the
plug is fully
inserted into the receptacle. However, the relay contacts can create sparks
that can ignite
explosive gas. Also, there is a race condition when the plug is removed. If
the relay contacts have
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not completely opened before the plug prongs disconnect from the receptacle
connections, a
spark can occur at the plug prongs. In addition, the plug is not locked into
the receptacle, so
unintended disconnection might occur.
[0010] US patent 4,995,017 describes a safety electrical receptacle and
claims to prevent
explosions. It uses a triac to block power from reaching the receptacle
terminals until a plug is
fully inserted. However, this design would not be safe or acceptable in an
atmosphere containing
explosive gas. There are switches and contacts in direct connection to the
high-voltage power
line. Any of these switches or contacts could cause a spark and a potential
explosion in the
presence of explosive gas.
SUMMARY
[0011] An electrical connector is disclosed comprising a receptacle having
openings, a
plug having blades that may be inserted into the openings in the receptacle,
elements on the
receptacle and on the plug having cooperating parts that create a first
disengagement stage of the
plug from the receptacle, in which removal of the blades from the openings
comprises a second
disengagement stage, a sensor arrangement sensitive to the first disengagement
stage to produce
a signal that energizes or de-energizes a relay; and the relay being
responsive directly or
indirectly to the signal to disable power to the electrical connector before
the second
disengagement stage, the relay having an isolation feature to prevent contact
of explosive gas
with a spark created by the relay. The cooperating parts may comprise a cover
for at least part of
the electrical connector that is movable between a covering position and an
uncovering position,
with the sensor arrangement comprising a first element on the cover and a
second element on one
of the plug and receptacle.
[0012] These and other aspects of the device and method are set out in the
claims.
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BRIEF DESCRIPTION OF THE FIGURES
[0013] Embodiments will now be described with reference to the figures, in
which like
reference characters denote like elements, by way of example, and in which:
[0014] Fig. 1 shows an electrical connector with a plug approaching a
socket, the
example shows a NEMA L21-30 twist-locking plug approaching a twist-locking
receptacle;
[0015] Fig. 1A shows a blade of the plug with twist lock element;
[0016] Fig. 2 shows the electrical connector of Fig. 1 with the plug
inserted in socket but
not locked;
[0017] Fig. 3 shows an electrical connector with a plug locked in socket;
[0018] Fig. 4 is a front view of a threaded socket, the example shows a
NEMA 5-15
electrical receptacle with male threads;
[0019] Fig. 5 shows a NEMA 5-15 electrical plug, with a locking nut
attached,
approaching the receptacle of Fig. 4, the locking nut having female threads to
mate with the
male threads on the receptacle;
[0020] Fig. 6 shows the electrical socket of Fig. 5 with fully inserted
plug and tightly
threaded socket;
[0021] Figs. 6A and 6B show respectively an encapsulated relay 610 and a
relay 610 in a
restricted breathing enclosure;
[0022] Fig. 7 shows a wiring block diagram of the electrical connector of
Figs. 1, 2 and
3;
[0023] Fig. 8 shows a wiring block diagram of the electrical connector of
Figs. 4, 5 and
6, including microprocessor controlling the relay coil based on input signals
from two magnetic
sensors; and
[0024] Fig. 9 shows a Timing Diagram 1 and Fig. 10 shows a Timing Diagram
2
showing the timing of signals for the system of Figs. 7, 8, and 9, with Time
on the X-axis and
Voltage on the Y-axis, in which Timing Diagram 1 shows signal timing when the
locking nut is
being rotated clockwise to tighten it and Timing Diagram 2 shows signal timing
when the
locking nut is being rotated counterclockwise to loosen it, and in which a
logic High level on the
signal from a magnetic sensor indicates that a magnet has been detected within
range of that
sensor.
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[0025] Figs. 11-14 show a further embodiment of an electrical connector.
DETAILED DESCRIPTION
[0026] An electrical connector is formed of a plug and socket or
receptacle. Design
features are disclosed to allow an electrical connector to be freely connected
and disconnected in
a hazardous location where explosive gas might be present. The disclosed
electrical connector
may use, along with the design features, standard NEMA electrical plugs and
receptacles,
including twist-lock designs such as NEMA L21-30 and NEMA L5-15, and straight-
blade
designs such as NEMA 5-15 types. The embodiments of Figs. 1-6 together with
the control
circuits are described and claimed in co-pending Canadian patent application
no. 2956033 filed
January 25, 2017.
[0027] The electrical connector with the design features is particularly
intended for Zone
2 and Class I Division 2 hazardous locations where explosive gas may be
present less than 10
hours per year. These hazardous locations comprise over 90 percent of the
hazardous locations in
most modern petrochemical facilities.
[0028] CSA Standard C22.2 No. 60079-15 Rule 20.1(a) defines the
requirements for
non-sparking plugs and receptacles in Zone 2 hazardous locations. The
electrical connector has
two stage design features that enable the electrical connector to meet this
CSA standard. The
electrical connector disconnects power from the receptacle unless the plug is
fully inserted and
locked into position in the receptacle. A sensor arrangement detects when the
plug is fully
inserted and locked. The sensor arrangement turns on a relay which allows
power to flow to the
receptacle and the connected plug. The relay is encapsulated in epoxy 612
(Fig. 6A) to keep
explosive gas away from the sparking relay contacts or may be otherwise
isolated from the
explosive gas. This method of protection for hazardous locations is allowed
under CSA Standard
C22.2 No. 60079-15 Rule 29. Various methods may be used to produce an
isolation feature to
prevent contact of explosive gas with a spark created by the relay, using a
material that forms a
barrier between metal contacts of the relay and the explosive gas. Fig. 6A
illustrates the relay
coil and relay contacts encapsulated in epoxy schematically and in practice
the components
would be mounted on a circuit board that would also be encapsulated in epoxy.
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[0029] Before the plug can be disconnected, it must be unlocked in a first
stage of
disengagement. The sensor arrangement detects the unlocking action and
releases the relay to
disconnect power from the plug and receptacle. The plug can then be removed
from the socket in
a second disengagement stage. No spark occurs at the connection between the
plug blades and
the receptacle contacts, because electrical power is not present at that
connection at the moment
of disconnection. Explosive gas is kept away from the spark that occurs at the
relay contacts by
epoxy that encapsulates the relay or another isolation feature.
[0030] An electrical connector is shown in Fig. 1, 2 and 3, with
corresponding electrical
block diagram of Fig. 7. In this design, a locking plug and receptacle such as
NEMA Type L21-
30, Type L5-15, or other NEMA twist-locking type are used. The plug 100 locks
into the
receptacle 140 by inserting the plug 100 into the receptacle 140 as shown in
Fig. 1 and Fig. 2,
and then twisting the plug 100 clockwise with respect to the receptacle 140 to
the position shown
in Fig. 3. At least one and usually each of the blades 110 of the plug 100
have a head 112 that is
longer in the circumferential direction than the stem 114 of the blade, as
shown in Fig. 1A. The
corresponding holes 152 in the receptacle 140 are enlarged in the same
circumferential direction.
These twist lock elements form cooperating parts on the plug 100 and
receptacle 140 that create
a first disengagement stage, with removal of the blades from the openings in
the receptacle
forming a second disengagement stage. The shoulder formed by the head creates
a stop that
abuts against a corresponding shoulder in the receptacle. The NEMA Type L21-30
electrical
connector has these features. A permanent magnet 130 is installed into a hole
near the face of
the plug 100. A magnetic sensor 160 is installed into a hole near the face of
the receptacle 140,
the sensor 160 and permanent magnet 130 together comprise an example of a
sensor
arrangement. For this design, a sensor that is sensitive to magnetic flux
perpendicular to the face
of the receptacle and insensitive to magnetic flux parallel to the face of the
receptacle is
preferred.
[0031] When the plug 100 is first inserted into the receptacle 140 to the
position shown if
Fig. 2, with its plug blades inserted in corresponding openings in the
receptacle 140, the magnet
130 and the sensor 160 are mis-aligned such that the sensor 160 does not
detect the presence of
the magnet 130. In this condition, the sensor 160 does not energize the relay
coil 660, the
normally-open relay contacts 670 remain open, and the Hot contact 150 in the
receptacle 140
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remains de-energized. When the plug 100 is twisted clockwise to lock it in the
receptacle 140 to
the position shown in Fig. 3, the magnet 130 on the plug 100 moves into
alignment with the
magnetic sensor 160 on the receptacle 140. The sensor 140 detects this
alignment and produces a
signal to energize the relay coil 660 to close the relay contacts 670 and thus
energize the contacts
150 in the receptacle 140 which are now connected to the blades 110 of the
plug 100. Two
distinct motions are required to insert the plug 100 into the receptacle 140,
when the relay
contacts 670 are open, and subsequently to twist the plug 100 to lock it into
the receptacle 140,
when the relay contacts 670 are closed. The receptacle contacts 150 and the
plug blades 110 are
not energized when they are joined together, so no arc or spark is caused. It
is only after the plug
100 is locked in the receptacle 140 that the receptacle contacts 150, the plug
blades 110, and
therefore the tool or appliance are energized.
[0032] To unplug the tool or appliance, the plug 100 is twisted
counterclockwise with
respect to the receptacle 140 to unlock it in a first disengagement stage This
action causes the
magnet 130 in the face of the plug 100 to become misaligned with the magnetic
sensor 160 in
the face of the receptacle 140. The sensor 160 de-energizes the relay coil
660, which causes the
relay contacts 670 to open. This de-energizes the receptacle contacts 150 and
the plug blades
110. A separate action or disengagement stage is required to pull the plug 100
out of the
receptacle 140. This action does not cause an arc, because the power to the
contacts was
disconnected during the unlocking action. This design is safe for use in Zone
2 and Class I
Division 2 areas containing explosive gas, because no spark is created upon
connection or
disconnection. As an added benefit, the twist-locking plug cannot be
inadvertently disconnected
from the receptacle. It requires two distinct motions to unlock and then
remove the plug from the
receptacle.
[0033] Fig. 7 shows a simplified wiring diagram for the system of Figs. 1,
2 and 3. Cable
120 supplies electrical power to the receptacle 140. Neutral and Ground
conductors from
incoming cable 120 are connected directly to the corresponding terminals on
the receptacle. The
energized wire, also called the Hot wire, might for example be energized at
120 Volts AC. The
Hot wire passes through a set of normally-open contacts 670 of relay 610
before it is connected
to the Hot terminal on the receptacle. When the coil 660 of relay 610 is
energized by placing a
DC voltage across it, the contacts 670 close, which causes the Hot terminal of
the receptacle to
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be energized. Magnetic sensor 160 energizes relay coil 660 when magnet 130 is
detected within
range of sensor 160. A power supply 650 converts AC voltage on the Hot and
Neutral wires of
cable 120 into DC voltage, for example 12 Volts DC, to supply power to the
sensor 160 and the
coil 660 of relay 610.
[0034] This design will often be used on three-phase power systems. In
that case there
are three energized (Hot) contacts in the receptacle, and three encapsulated
relays are used to de-
energize the Hot receptacle contacts, with one relay controlling each phase.
[0035] The relays may be installed in a Restricted Breathing enclosure
614, shown
schematically in Fig. 6B, another form of spark prevention feature. In
practice, the Restricted
Breathing enclosure will normally enclose the entire circuit board, with relay
mounted on the
circuit board. The Restricted Breathing enclosure performs the same function
as the
encapsulation of the relay and other electrical components on the circuit
board. Both methods
keep explosive gas away from the arcing relay contacts and thus prevent
explosion if explosive
gas is in the atmosphere. Both Restricted Breathing and Encapsulation are
acceptable protection
methods for arcing and sparking components in Zone 2 hazardous locations as
defined in CSA
standard C22.2 No. 60079-15.
[0036] Another design is shown in Figs. 4, 5 and 6, electrical block
diagram Fig. 8, and
Figs. 9 and 10 (Timing Diagrams 1 and 2). Referring to Fig. 5, a weatherproof
NEMA 5-15 or
other NEMA standard plug 100 has a captive nut 180 with internal threads which
are tightened
onto male threads 200 on the mating receptacle 140 to prevent water from
entering the
connection. The threads on the nut and the male threads 200 are designed such
that the nut can
rotate at least two full turns from completely loose to completely tight. The
nut 180 is free to
rotate around the plug 100, but has very limited range of motion forward and
backward along the
plug. A commercially available plug of this type is Leviton part number LNR80-
1E. The mating
threaded receptacle is Leviton part number LNR96-1. The threads and nut form
cooperating parts
that create a first disengagement stage. The nut may instead be placed on the
receptacle with the
exterior threads on the plug.
[0037] To modify the commercially available products for this design, a
permanent
magnet 130 is embedded into the captive nut 180 on the plug 100, and two
magnetic sensors
160-1 and 160-2 are embedded in the receptacle 140 near the male threads 200.
Fig. 4 is a front
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view of the receptacle 140 that shows the approximate relative position of the
two sensors 160-1
and 160-2 in the receptacle 140. The sensors 160-1 and 160-2 are approximately
20 degrees apart
near the circumference of the receptacle threads 200. Sensor 160-1 is
counterclockwise from
sensor 160-2 in Fig. 4. Also shown in Fig. 4 are the contacts 150 in the face
of the receptacle
140. The sensors 160-1 and 160-2 and the circuitry of Fig. 8, other than the
relay 610, form a
sensor arrangement that is sensitive to the positioning of the nut to energize
the relay and allow
power to flow in the electrical connector.
[0038] When the plug 100 is plugged into the receptacle 140 before
rotation of the nut
180 to the position shown in Fig. 6, the receptacle contacts 150 and the plug
blades 110 are de-
energized because the relay contacts 670 are open. The captive nut 180 on the
plug 100 must be
tightened onto the male threads 200 on the receptacle 140 before the relay 610
is energized to
close the relay contacts 670 and thus energize the receptacle contacts 150 and
the plug blades
110.
[0039] On Figures 9 and 10, time is on the x-axis and voltage is on the y-
axis. Fig 9
shows the signal 210 from sensor 160-1, the signal 280 from sensor 160-2, and
the signal 340 to
the relay coil 660 of relay 610 at a time when the captive nut 180 is being
tightened onto the
male threads 200 to secure the plug 100 to the receptacle 140. The nut 180 is
rotated clockwise
to tighten. The magnet 130, secured to the nut 180, moves into alignment with
sensor 160-1 at
time 220, and the output signal 210 from sensor 160-1 goes High to indicate
that the magnet 130
has been detected. Magnet 130 continues to move past sensor 160-1 until time
230 when magnet
130 is out of alignment with sensor 160-1, and signal 210 from sensor 160-1
goes Low to
indicate that magnet 130 is not sensed. As the nut 180 continues to rotate
clockwise, a short time
later at time 290 the magnet 130 moves into alignment with sensor 160-2.
Signal 280 from
sensor 160-2 goes High to indicate that the magnet 130 has been detected.
Magnet 130
continues to move past sensor 160-2 until time 300 when magnet 130 is out of
alignment with
sensor 160-2, and signal 280 from sensor 160-2 goes Low to indicate that
magnet 130 is not
sensed. In this way, a pulse from sensor 160-1 is followed a short time later
by a pulse from
sensor 160-2 when the nut 180 is tightened. This sequence is repeated starting
at time 240 and
again starting at time 260 as tightening continues. The difference between
time 220 and time 240
and between time 240 and time 260 is the time required for one complete
revolution of nut 180.
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[0040] When the nut 180 has been tightened for at least one complete
revolution, the
engagement of the threads on the nut with the male threads on the receptacle
makes it impossible
to remove the plug from the receptacle. This condition occurs at time 240, and
at this time it is
safe to energize receptacle contacts 150 and plug blades 110, because they can
no longer be
disconnected to cause a spark. A microprocessor 680 is configured according to
the timing
diagrams of Figs. 9 and 10 to detect the output of sensors 160-1 and 160-2 and
determines
direction of rotation of the nut 180. If the sequence of pulses indicates
clockwise rotation of nut
180 as shown in signals 210 and 280, the microprocessor causes the coil 660 of
relay 610 to
become energized at time 240. This closes the relay contacts 670 to energize
the receptacle
contacts and plug blades, and thus the tool or appliance connected to the plug
by cord 120
becomes energized.
[0041] At some time after time 240, clockwise rotation of nut 180 stops
because the nut
is tight. The microprocessor 680 stores the state of the relay coil output 340
in non-volatile
memory and retains the relay coil output in the same High state until some
later time when the
nut is loosened. Power is allowed to flow to the tool or appliance as long as
the nut is tight.
[0042] Fig 10 shows the sequence of pulses from the two sensors 160-1 and
160-2 as the
nut 180 is being loosened by rotating it counterclockwise. The magnet 130
embedded in the nut
180 moves into the detection range of sensor 160-2 at time 420, and the output
280 of sensor
160-2 changes to a High state. As the nut continues to rotate
counterclockwise, the magnet 130
moves out of range of sensor 160-2 at time 430, and the output 280 of sensor
160-2 changes to a
Low state. As the nut 180 continues to rotate counterclockwise, a short time
later at time 360 the
magnet 130 moves into alignment with sensor 160-1. Signal 210 from sensor 160-
1 goes High to
indicate that the magnet 130 has been detected. Magnet 130 continues to move
past sensor 160-
1 until time 230 when magnet 130 is out of alignment with sensor 160-1, and
signal 210 from
sensor 160-1 goes Low to indicate that magnet 130 is not sensed. In this way,
a pulse from
sensor 160-2 is followed a short time later by a pulse from sensor 160-1 as
the nut 180 is
loosened. This sequence is repeated starting at time 440 and again starting at
time 460 as
loosening continues.
[0043] In summary, when the nut is being tightened, sensor 160-1 emits a
High pulse
before sensor 160-2. When the nut is being loosened, the pulse sequence is
reversed.
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[0044] When microprocessor 680 detects the sequence of pulses on signals
210 and 280
that indicates loosening of nut 180 has begun as shown in Fig 10, the
microprocessor causes the
coil 660 of relay 610 to become de-energized at time 480. This opens the relay
contacts 670 to
de-energize the receptacle contacts and plug blades, and thus the tool or
appliance connected to
the plug by cord 120 becomes de-energized. This occurs some time before the
threaded ring is
completely unthreaded from the receptacle. Power is removed from the
receptacle and the plug
before it is possible to remove the plug from the receptacle. Since the
contacts are not energized
when it is finally possible to separate the plug from the receptacle, no spark
will be created.
Sparks may occur inside the relay when the contacts are switched, but the
relay is encapsulated
in epoxy to keep explosive gas away from the spark. This design is therefore
safe for use in an
area that may contain explosive gas.
[0045] Fig. 8 is an electrical block diagram for the system of Figs. 4, 5
and 6. It shows
the microprocessor 680 receiving signal 210 from sensor 160-1 and signal 280
from sensor 160-
2. The microprocessor analyzes the pulse sequences from the two sensors, and
determines
whether the nut 180 is rotating clockwise, rotating counterclockwise, or
stationary according to
Figs 9 and 10. The microprocessor outputs signal 340 to control the relay coil
660 and thus the
contacts 670 of relay 610. The relay contacts allow the Hot contact 150 of
receptacle 140 to be
energized according to signal 340 of Figs 9 and 10.
[0046] The relay may be installed in a Restricted Breathing enclosure. The
Restricted
Breathing enclosure performs the same function as the encapsulation of the
relay. Both methods
keep explosive gas away from the arcing relay contacts and thus prevent
explosion if explosive
gas is in the atmosphere. Both Restricted Breathing and Encapsulation are
acceptable protection
methods for arcing and sparking components in Zone 2 hazardous locations as
defined in CSA
standard C22.2 No. 60079-15.
[0047] The magnetic sensor 160 may be replaced by a reflective optical
sensor and the
magnet 130 can be replaced by a reflector. A sensor arrangement may also use a
reflective
optical sensor, in which, in place of magnet, a reflector is used. The sensor
detects light only
when reflected back from reflector to sensor.
[0048] When a magnetic sensor is used in the sensor arrangement, a piece
of steel may be
used to steer away unwanted magnetic flux. The steel goes counterclockwise
from the sensor, as
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seen from the plug end. It sits about as far from the magnet when the plug is
unlocked as the
sensor does, but in the opposite direction rotationally. Flux from the magnet
will tend to move in
the direction of the steel, not the sensor. As the plug is locked, the magnet
moves away from the
steel and toward the sensor. This should increase the discrimination of the
sensor between
unlocked and locked. It may be better to use a more sensitive sensor if the
sensor is not as
affected by stray flux. Equipment for use in hazardous locations must not
produce sparks that can
ignite explosive gas.
[0049] An electrical receptacle with a releasable locking mechanism is
described in US
patent 5,921,799, and other examples exist in the prior art. The locking
receptacle accepts a
standard NEMA 5-15 plug as found on most 120 Volt electric tools and
appliances in North
America that draw up to 15 Amperes. The plug is locked into the receptacle
until a locking ring
is moved away from the plug.
[0050] Referring to Figs. 11-14, the cooperating parts may comprising a
cover for at least
part or all of the electrical connector, for example, the plug. The cover may
be movable for
example by rotation about a hinge 175 or by a translation or sliding movement,
between a
covering position and an uncovering position. If a translation or sliding
motion is used,
cooperating rails or tracks may be provided on the respective components to
allow the cover to
move between closed and open positions. In the embodiment of Figs. 11-14, the
electronic
control circuits of Fig. 7 may be used, although if a second sensor is used on
the receptacle,
control circuits of Fig. 8 and the timing diagrams of Figs. 9 and 10 may be
used.
[0051] A sensor arrangement may a first element (magnet or sensor) on the
cover and a
second element (sensor or magnet) on one of the plug and receptacle. In the
example of Figs. 11-
14, a hinged cover 170 is normally lowered over the receptacle 140 to protect
it from rain in the
covering position. A permanent magnet 130 is attached to the hinged cover 170.
A magnetic
sensor 160 is attached to the enclosure near the receptacle 140. The magnetic
sensor 160 detects
the presence of the magnet 130 when the hinged cover 170 is lowered into its
closed position.
The cover 170 must be lifted before the plug 100 can be inserted into the
receptacle 140 (first
disengagement stage). The sensor 160 detects that the magnet 130 has been
removed, indicating
that the cover 170 has been lifted. The sensor 160 responds by opening the
relay contacts 270 to
de-energize the Hot contacts 150 in the receptacle 140. The relay 610 is
encapsulated in epoxy or
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enclosed in a Restricted Breathing Enclosure. The epoxy or enclosure keeps
explosive gas away
from any arc that might occur at the relay contacts 270.
[0052] Referring to Fig. 12, when the plug 100 is inserted and locked into
the receptacle
140, the contacts 150 are still de-energized, so no spark can occur as a
result of insertion of the
plug 100. Referring to Fig. 13, the hinged cover 170 is lowered into the
closed position over the
plug 100 and the attached cord 120. The hinged cover 170 has a slot in the
bottom to allow the
cord to exit. The sensor 160 detects the presence of the magnet 130, which
indicates that the
hinged cover 170 is closed. The sensor 160 activates the relay 610 to close
the relay contacts
270. Thus the receptacle contacts 150 are energized. This allows the electric
tool or appliance
connected to the plug 150 to operate.
[0053] To unplug the tool or appliance, the hinged cover 170, with magnet
130 attached,
must be lifted to the position shown if Fig. 12. When this occurs, the
magnetic sensor 160 detects
that the magnet 130 is not within range of the sensor 160. The sensor 160
causes the relay
contacts 270 to open, thus de-energizing the receptacle contacts 150. Any arc
in the relay
contacts 270 is kept away from explosive gas by the epoxy that encapsulates
the relay 610. The
locking mechanism in the receptacle 140 must then be released to allow the
plug 100 to be
removed. No arc occurs when the plug blades 110 are separated from the
receptacle contacts
150, because both are de-energized at the time of separation. Unintended
disconnection of the
plug 100 from the receptacle 140 is prevented by the locking design of the
receptacle 140.
[0054] One advantage of this embodiment is that the plug on the tool or
appliance to be
energized is a standard NEMA 5-15 plug. This is the plug normally used on 120
Volt tools and
appliances in North America. There is no need to change the plug on the tool
to make it safe for
use in hazardous locations that may contain explosive gas. Connection and
disconnection of the
plug takes place when the receptacle is de-energized, so no arc will occur as
a result of
connection or disconnection.
[0055] In an alternate version of this embodiment, the relay is installed
in a Restricted
Breathing enclosure as defined in CSA standard C22.2 No. 60079-15 Rule 31. The
enclosure
keeps explosive gas away from any arcing or sparking contacts. This makes this
embodiment
safe for use in Zone 2 hazardous locations that may contain explosive gas
occasionally. Both
Restricted Breathing and Encapsulation are acceptable protection methods for
arcing and
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sparking components in Zone 2 hazardous locations as defined in CSA standard
C22.2 No.
60079-15.
[0056] A system is described which allows extension cords and power cords
from
electric tools to be plugged into and unplugged from a power source without
causing electrical
arcs or sparks. This system will be particularly useful in permanent and
temporary power
installations on single-phase and three-phase circuits rated at 120 Volts AC
or higher and 15
Amperes or higher in Zone 2 and Class I Division 2 hazardous locations.
[0057] The electrical connector may be used for inexpensive electrical
plugs, receptacles
and extension cords that are safe for use in Zone 2 and Class I Division 2
hazardous locations.
Objectives and advantages of the disclosed embodidesigns ments may include one
or more of the
following:
a. 1) Electrical plugs, receptacles, and extension cords can be freely
and safely
connected and disconnected in Zone 2 hazardous locations, even under
load.
i. No electrical arcs and sparks are created when a plug is inserted and
removed from a receptacle.
ii. Industry-standard NEMA plugs and receptacles may be used with
modifications such as disclosed. These NEMA devices are inexpensive
and readily available.
iii. Operation is safe in Zone 2 and Class I Division 2 hazardous locations
where explosive gas might be present up to 10 hours per year.
iv. Plugs and receptacles can be connected and disconnected without the need
to determine if explosive gas is present. No special warning labels are
required for use in hazardous locations.
v. The requirements of safety certification standards such as CSA C22.2 No.
60079-15, C22.2 No. 60079-0, and C22.2 No. 213 may be met.
vi. A receptacle is not energized unless a plug is fully inserted and locked
into
place.
vii. The plug locks into the receptacle. Unintended separation is prevented.
The action of unlocking the plug from the receptacle causes the power to
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be disconnected from the receptacle. Power is disconnected before the
plug can be removed from the receptacle, so no spark is created.
[0058] Immaterial modifications may be made to what is described here
without
departing from what is covered by the claims. In the claims, the word
"comprising" is used in its
inclusive sense and does not exclude other elements being present. The
indefinite article "a"
before a claim feature does not exclude more than one of the feature being
present. Each one of
the individual features described here may be used in one or more embodiments
and is not, by
virtue only of being described here, to be construed as essential to all
embodiments as defined by
the claims.
